Distillation,Summary
Distillation is a widely used separation
process.
The separation is based on the volatility
difference of the components to be
separated.
Wide application of distillation,
WHY?
Volatility difference exists for most
mixtures.
Only heat is needed for the separation,no
other extra agents are needed,So the
products may be pure.
Classification of distillation
Relative Volatility Process Example
big Equilibrium
distillation or flash
distillation
H2 and oil
medium fractionation Benzene
and tolune
small Azeotropic
distillation and
extractive distillation
Absolute
ethanol
production
1
2
3
4
Flash distillation
T
xAor yA
dew point line
bubble point line
Fractionation with
rectifying section and stripping section
column with rectifying section and stripping
section
condenser(total and partial),accumulator,
cooler,cold water
reflux and overhead product
reboiler,steam and condensate
bottom product
Equipment to implement
distillation process
Plate tower or column
Packed tower or column
Structure of plate tower
sieve plate;
perforations;
downcomer;
weir.
Calculation of distillation process
minimum reflux ratio
minimum number of trays
optimum reflux ratio and number of plates
McCabe-Thiele method
for the calculation of
theoretical tray number
equilibrium stage assuption (ideal stage)
constant molar overflow assumption
operating line and equilibrium curve
feed line
Efficiency
Reason,ideal plate assumption is not true
because of not enough contact,
Overall efficiency
Murphree efficiency
Transfer phenomena in plate tower
Mass transfer,
– light component,from liquid to vapor
– heavy component,from vapor to liquid
Heat transfer:
– from vapor to liquid (?)
Fluid flow:
– liquid,based on the gravity
– how the liquid comes to the high position? Vapor
– how comes the vapor flow? Pressure difference.
– How comes the difference? The reboiler and steam.
System design of multi-
component mixture
Continuous operation
– n components
– n-1 tower
– n pure products
Batch operation
Continuos distillation and batch
distillation
Batch distillation,differential distillation
– without stripping section
Other aspects of distillation
Azeotropic distillation
Benzene as azeotropic agent
A new azeotropic mixture forms
Water is becoming more volatile than
without azeotropic agent
Separation factor? becomes larger.
Azeotropic distillation
1
BEWWEB
2 3
0.89
EW
99.9%
E
EWB
EWB
E
W
99.9
%W
0.89
EW
B,benzene
E,ethanol
W,water
EWB,azeotropic
EW,azeotropic
Extractive distillation
Salt or glycol is added as extraction agent
water is becoming less volatile than without
extraction agent
separation factor? becomes larger.
Extractive distillation
1 20.89 EW
99%
E
W G
G
W
E,ethanol
W,water
G,glycol
Other Aspects of Distillation:
Eg 1 Steam distillation
feed
Bottom product
steam
overhead
reflux
Reboiler is saved!
Other Aspects of Distillation:
Eg 2 Heat pump technology
Overhead ;
condenser;
remove heat
!
! compressor
bottom; reboiler; add heat
Other Aspects of Distillation:
Eg 3 Reaction distillation
Esterification reaction
Ethanol + Acetic acid? Ethyl acetate + water
reactor separationsystem
water
acetate
ethanol
ethanol
Acetic acid
water
ester
ethanol
water
Acetic acid
Ethanol
(vapor)
A.A + A = E + W